Conventional wisdom suggests that more carbon dioxide is good for plants because they breathe carbon dioxide. A recent study by a University of California scientist has found that increases in atmospheric CO2 could actually be bad news for crops.
A field test showed that higher carbon dioxide levels inhibit plants’ ability to turn nitrate into proteins, indicating that food quality could be at risk from climate change. In fact, food quality has declined as atmospheric CO2 has gone up, according to the lead author of the study, Arnold Bloom. Bloom is a faculty member of the University of California – Davis Department of Plant Sciences.
Bloom reported that this is the first time a study of field-grown crops has been conducted in an effort to see if there is a link between increasing carbon dioxide levels and nitrogen assimilation. Nitrogen processing is critical to plant growth, and to food production. Plants must use nitrogen to create proteins that humans need to survive. Wheat, for example, provides nearly 25 percent of the protein that humans consume globally.
Previous laboratory studies had shown that increased levels of atmospheric carbon dioxide inhibited nitrate assimilation in some grains and non-legumes, but no one knew if this phenomenon would occur in an uncontrolled environment, like a farm field.
Bloom and his colleagues spent more than 10 years monitoring wheat fields exposed to differing carbon dioxide levels. Different sections of the field were treated with different amounts of supplemental CO2 or left alone as an experimental control. Analysis of the wheat did show that nitrate assimilation was inhibited by higher concentrations of CO2 in the atmosphere.
Bloom noted that other studies reported a loss of protein in crops like barley, rice, wheat, and potatoes of about eight percent with elevated carbon dioxide levels. Because those crops account for such a large fraction of human food consumption, the overall amount of protein available could drop by three percent in coming decades.
Those results show that carbon dioxide could be bad news for food crops.
The UC-Davis study was published online April 6 in Nature Climate Change. The results are at odds with other work on climate science.
A report to be released by the Heartland Institute, a Chicago, IL libertarian think tank, on April 9 claims that carbon dioxide would be good for the planet, leading to more forest and plant growth, longer growing seasons, and higher crop yields. The 150-page report reviews studies of climate change, some published in the 1980s. Heartland stated that the Intergovernmental Panel on Climate Change ignored those studies when preparing its recent reports on the dire consequences of climate change.
Critics of the Heartland Institute analysis point out that plants grow best at an optimal temperature and respond poorly when temperatures vary above or below that range. Increasing yields due to warmer weather may be mostly or entirely erased if the temperature goes up more.
Paul Gepts, professor of Plant Sciences at the University of California – Davis said that whatever benefit may come from increasing CO2 levels could be erased by rising temperatures. Just a small change in temperature can produce a big disruption in food production. Bean production, for example, may move north from the Upper Midwest into Canada, as temperatures rise and old bean-growing areas become less viable.
Global warming could also release carbon dioxide from the frozen tundra of Alaska, Canada, and northern Russia. The carbon dioxide, so the argument goes, would fuel greater plant growth. This is true to a limited extent, but the ground releases more CO2 than the plants can absorb, says Susan Natali, associate scientist at the Woods Hole Research Center.
In their report, the Heartland Institute notes that the more carbon dioxide there is, the better plants grow. Increasing temperatures would extend to growing season and open up new areas to certain crops. For example, North Dakota is in the Corn Belt now.
Both the University of California and Heartland reports come in the wake of a huge new report on the risks of climate change released by the United Nations Intergovernmental Panel on Climate Change. That study pointed to massive potential disruptions in food production, coastal communities, and global weather patterns over the rest of the century.
More carbon dioxide in the air means more plant growth, but the news on balance is bad. Increasing levels of carbon dioxide in the atmosphere will be bad news for crops and may not open up new lands for cultivation.
By Chester Davis